Hinge axis locating apparatus



p 17, 1957 c. E. STUART 2,806,284

HINGE AXIS LOCATING APPARATUS Filed March 15. 1956 IN VEN TOR. CHARLES E. STUART A TTORMEKS 2,806,284 Patented Sept, 17, 1957 HENGE AXIS LOCATINGAPPARATUS Charles E. Stuart, Ventura, Calif.

Application March 13, 1956, Serial No. 571,312

2 Claims. (Cl. 32- 20 This invention relates broadly to an apparatus for locating the hinge axis of a movable member with respect to a stationary reference. More particularly, it has to do with a system for rapidly ascertaining the hinge axis of a persons mandible or lower jaw in order to facilitate the fabrication of dentures and the like.

During the course of dental treatment, it is oftentimes necessary to make transfers of models and the like formed from impressions of the human mouth to an instrument which reproduces the movements of the mandible. Such an instrument is known in the art as an articulator. It is extremely important that the hinge axis for the mandible counterpart of the instrument be precisely located with respect to the remaining counterparts of the mouth in order that movements of the lower jaw are accurately represented.

Inlocating the hinge axis of the mandible, it has been common practice to employ a face bow, the front portion of which is rigidly affixed to a portion of the lower jaw. The rearwardly extending portions of the bow pass on either side of the persons face and are provided with adjustable styli which may be positioned to point at the location on the two sides of the persons face through which hinge axis passes. In determining these points, the patient actuates his lower jaw to swing the face bow in generally arcuate movements and the styli points are adjusted by trial and error until they exhibit only a rotational motion with no translation components. When the styli are adjusted to this position, they then coincide with the mandible hinge axis. These points may be marked on the persons face as by tattooing, for example, so that relocation of the hinge axis during subsequent transfers may be readily achieved. Alternatively, an axis orbital plane recorder such as described in my co-pending application, Serial Number 498,353, filed March 31, 1955, and entitled Axis-Orbital Plane Recorder may be used. In either event, the problem of initially locating the hinge axis is still a matter of trial and error.

Bearing the above in mind, it is a primary object 'of the present invention to provide an apparatus which enables the hinge axis of a persons mandible to be rapidly ascertained without the necessity of constantly readjusting stylus points, as is necessary in the case of a trial and error procedure.

A further important object is to provide, in combination with the hinge axis locator, an improved axis-orbital plane recorder which will enable the hinge axis of a persons mandible to be relocated with consistent accuracy of high degree.

Briefly, these and other objects and advantages of the present invention are attained in the case of dental work by providing an apparatus including a closed grid surface adapted to be fixed to a frame positioned on a persons head to serve as a stationary reference. The closed grid is of sufficient area to enable it to be easily positioned over a region which will include the hinge axis of the mandible. A co-operating open grid surface is adapted to be rigidly fixed to the mandible as by means of a face bow and positioned substantially to overlie the closed grid so that movement of the mandible results inrelative movement between the closed grid and the open grid. The arrangement is such that by sighting through the open grid and observing the closed grid during the actuation of the mandible, the hinge axis may be instantly ascertained and subsequently recorded on the closed grid by a suitable marking. Subsequent relocation of the hinge axis is readily accomplished by simplyrepo'sitioning the stationary reference frame and observing the position of the marked point on the closed grid surface;

A better understanding of the invention and its pre-. ferred application in dental work will be had by referring to the accompanying drawings, in which:

Figure 1 is a general perspective view of the apparatus of this invention in position on a persons head;

Figure 2 is a plan view of one portion of the apparatus;

Figure 3 is an enlarged end view of the apparatus taken in the direction of the arrow 3 of Figure 1; and,

Figure 4 illustrates, partly in plan and perspective view,

one type of face bow for facilitating transfer of the hinge axis data from a persons head to an articulator.

Referring to Figure 1, there is shown a reference frame structure 10 having a straight front portion 11 and rearwardly extending portions 12 and 13 passing on opposite sides of a persons face. A flexible cross bar 14 is arranged to pass behind the persons head to be received in suitable notches 15 in the rearwardly extending portions of the frame.

The reference frame 10 is designed to enable it to be consistently positioned at the same place on a persons head by a nose piece 16 on the straight portion 11 and an orbital plane locator comprising a supporting block 17 having a bore through which the straight portion 11 passes. The block 17 may be moved axially with respect to the straight portion 11 of the frame and secured in a set position by a set screw 18. The front portion of the block 17 is provided with a vertical bore through which passes an orbital plane locating stylus 19 movable through the block 17 to different vertical positions and adapted to be set by a set screw 20. Preferably, the locating stylus 19 is provided at its upper end with a scale 21 whereby its vertical position within the block 17 may be consistently relocated after the point of the locator has been positioned at the base of the persons orbital plane. V

In accordance with an important feature of the invention, there is provided .on each side of the reference frame 10 a slide block such as the slide block 22 on portion 12 adapted to be set in any desired position by a set screw 23. A recording side plate having a closed grid surface 24 is secured to the slide block 22 as shown. A similar slide block and closed grid surface are also provided on the rearwardly extending portion 13 as best seen in Figure 2.

Co-operating with the reference frame 10 for determining the hinge axis of the persons mandible is a face bow 25 having a securing plate 26 adapted to be rigidly affixed to the persons mandible whereby the front portion of the face bow 25 will follow themovement of the lower jaw. The rearwardly extending portions of the face bow 25 are each provided with a support block 27 positionable on the bow by a set screw 28 for supporting a sighting tube 29 having an open grid network 30. The face bow 25 is shaped such that the sight tube 29 may be positioned to cover a portion of the closed grid 24 so that the closed grid may be seen through the open grid 30 as clearly indicated in Figure 3.

In operating the apparatus for locating the hinge axis of the persons mandible, the reference frame is first positioned on the persons head, the nose piece 16 fitting in the nasion and the rearwardly extending portions 12 and 13 passing within the creases between the upper portion of the ear's and the sides of the head. The cross bar 14 is then positioned in a suitable notch 15 to securely hold the referenceframe to the persons head. V

The orbital plane locator 19 is then positioned to point at the lower edge or border of the orbit and the various sets crews tightened. The dimensioning and arrangement of the reference frame 10 and the corresponding closed grid surfaces 24 on each of the rearwardly extending portions is such that the closed grids may be positioned to cover a region on the sides of a persons face which includes the mandible hinge axis even though the precise locationof this hinge axis is not known. This hinge axis is designated A-A in Figure 1.

The face bow .25-is then affixed m the persons mandibleand each sightingtube 29 adjusted by its corresponding support block 27 until it covers a substantial portion of the closed grid surface. The doctor or operator then observes the closed grid 24 through the sighting tube and through the open grid 30, as shown in Figure 3, and instructs the patient to actuate his mandible. Actuation or movement of the mandible is caused to take place in its most rearward position and will cause the open grid network 30 to move with respect to the stationary closed grid surface 24 such as indicated by the dotted lines in Figure 3. The "center of rotation may be immediately ascertained by sighting through the open grid inasmuch as no translation of those grid squares at the center of rotation will occur. In Figure 3, as an example, the center of rotation has, been ascertained to lie at the point P and the hinge axis thus passes through this point. The doctoror operator of the device then simply marks with Pencil through, the'open grid 30 the point on the closed grid 24 corresponding to the point P.

The sighting tubes 29 and support blocks 27 may then be removed from the face bow 25 and suitable stylus support blocks such as the blocks 31 illustrated in Figure 4 aflixed to the face bow. Each of the blocks 31 includes a set screw 32, for positioning the block on different portions of the rearwardly extending parts of the face bow, and suitable styli 33 vertically positionable within the blocks and capable of being set at any desired position by set screws 34. With this arrangement, it isasimple matter to adjust the points of the styli 33 to point precisely at the respective points, such as the point P on each. of the closed grids 24. The set screws 32 and 34 are then tightened and the face bow may then be transferred to the articulator to accurately locate the hinge axis of the mandible counterpart.

It will be noted in Figure 3 that the side plate having the closed grid surface 24 inscribed thereon also includes room for writing in data concerning the position of the mandible hinge axis of the particular patient under consideration; Thus, for example, the plate will include identifying data as to the patient as well as the various settings for the axis orbital plane locator 19, and the slide blocks 22 with respect to a scale 36 on the frame 10. These members may thus be readily repositioned. It is, therefore, an easy matter to relocate the mandible hinge axis on the patient at a subsequent date without the tracessity of tattooing or following through a trial and error method each time. In other words, once the settings have been. re-established on the fixed frame, the point P on the closed grid surface 24 will coincide with the mandible hinge axis.

The same reference frame may, of course, be employed for diflferent patients, the side plates with the closed grid surfaces 24 being individual to each patient and exchangeable with side pates having identifying data for the particular patient under consideration. With the data set forth at 35 on the particular side plate used, it is a simple matter to readjust the axis orbital plane locator 19 and the slide blocks 22 as well as the rear cross bar 14 such that the point on the new closed grid will coincide with the new mandible hinge axis.

While the face how 25 has been described as serving the dual function of alternately supporting the sighting tubes 29 and the stylus locators 33, it is, of course, possible to employ a separate face bow carrying the stylus locators 33.

It is apparent from the above description that the present invention provides an extremely rapid and simple means for finding the hinge axis of a persons lower jaw without having to proceed through a lengthy trial and error method, and that once the hinge axis is located, relocation thereof at subsequent periods is extremely simple. Furthermore, as mentioned above, the same apparatus may be used for many different patients, only the side plates and accompanying data on the closed grids being substituted in accordance with the particular patient involved.

Minor modifications within the scope and spirit of the present invention will occur to those skilled in the art. Further, while the apparatus has been described in connection with the locating of a persons mandible hinge axis, the system is readily susceptible to the problem of locating any hinge axis of a movable member with respect to a stationary reference. The principles involved, therefore, are not to be thought of as limited to the specific application described and shown for illustrative purposes.

What is claimed is:

1. An apparatus for locating the hinge axis of a persons mandible comprising, in combination: a reference frame adapted to be positioned about a portion of said persons head; said reference frame including a nose piece and an orbital plane locating device secured to its front portion; an orbital plane scale means associated with said orbital plane locating device, said frame having rearwa'rdly extending portions adapted to seat within the crease between said persons ears and the sides of said persons head, said rearwardly extending portions each having a series of longitudinally spaced transverse notches; a cross bar adapted to seat in said notches whereby said reference frame may be consistently positioned on said persons head in accordance with indications obtained from said orbital plane scale means and the notches in which said cross rod is seated; two recording side plates having closed grid surfaces carried on opposite sides of said persons face by said reference frame, said side plates covering regions on the sides of said persons head including said hinge axis; a face bow adapted to be rigidly secured to said persons mandible and having portionsextending rearwardly on opposite sides of said person's face to positions adjacent said side plates; and open grid networks secured to said portions of said face bow in spaced substantially parallel relationship to said closed grids so that actuation of said mandible rotates said open grids with respect to said closed grids whereby the center of rotation and thereby the hinge axis of said mandible may be ascertained by observing the relative rotational motions of said grids.

2. Anapparatus according to claim 1, including means for adjustably positioningsaid side plates on said reference frame; and scales-associated with said means whereby said side plates may be consistently repositioned in accordance with indications obtained from said scales.

References Cited in the file of this patent UNITED STATES PATENTS 1,705,223 McLean Mar. 12, 1929 

